My son has a mountain bike with extremely knobby 26 x 2.10 tires. He is interested in mounting some smooth tires for use on roads and MUPS around town. I don't know much about tires but I have learned that my 700 rims can take a wide range of tire sizes from probably around 28c up to 35 or maybe even 38c. My son has 26" Bontrager Maverick rims. I assume he can mount a variety of tire widths. How do we figure out what the range is? Any optimum tire size for around town, flat surface cruising?